Polarizable ferroelectric ceramic compositions



3,463,732 POLARIZABLE FERROELECTRIC CERAMIC COMPOSITIONS l-Iisao llanno,Aichi Prefecture, and Tsutomu Tsunooka, Kuriya, Japan, assignors to NGKSpark Plug Co., Ltd., Nagoya, Japan No Drawing. Filed July 5, 1967, Scr.No. 651,112 Claims priority, application Japan, Au". 26, 1966, 41/55,798 Int. Cl. C(Mb 35/00, 35/46; H01v 7/02 US. Cl. 25262.9 26 ClaimsABSTRACT OF THE DISCLOSURE A novel and useful polarizable ferroclectricceramic composition suitable for use in piezoelectric andelectrostrictive ceramic articles and consisting essentially of a seriesof solid solutions expressed by the formula,

Pb(W hla g) wherein Ma represents at least one clement selected from thegroup consisting of Ni and Zn, or another series of solid solutionsexpressed by taining Mn at a rate corresponding to up to 5.0 Weightpercent of MnO in the aggregate.

This invention relates broadly to compositions of mat ter and articlesof manufacture fabricated therefrom.

More particularly, the invention pertains to novel ferroelectricceramics susceptible of electrostatic polarization and exhibiting, whenpolarized, electromechanical transducing properties similar to thewell-known piezoelectric effect. As a result of these properties,materials, of the type to which the present invention pertains have cometo be known and may hereinafter be referred to as piezoelectricceramics. \Vhile the principal product contemplated by the invention isthe matured and polarized ceramic, as well as articles fabricatedtherefrom, it is to be understood that it also encompasses asintermediates the unreacted physical mixture of raw materials and theheat reaction product of such mixtures. Accordingly, the term ceramiccompositions will be used herein to encompass and designate genericallythe compositions of matter at all stages from the unreacted physicalmixtures to the matured and polarized ceramic which is the ultimateproduct.

Polarizable ferroelectric ceramic compositions for use in piezoelectricand electrostrictive elements have a perovskite structure expressed bythe formula ABO wherein A represents a bivalent metal ion and Brepresents a four valent metal ion. But, all of the compounds having theperovskite structure do not always exhibit piezoelectric andelectrostrictive properties. Some of them such as barium titanate, BaTiOsingly exhibit piezoelectric and electrostrictive properties, another ofthem such as lead titanate zirconate, PbTiO PbZrO do not individuallyexhibit, as lead titanate and lead zirconate, piezoelectric andelectrostrictive properties, but as a solid solution of at least two.for example, two of them exhibit piezoelectric 3,463,732 :ntecl Aug. 26,1969 and electrostrictive properties, whilst ABO structure wherein Brepresenting four valent ion consists of two ions having different ionicvalency such as Mifg-MZE or Mfg-M2,;

wherein M M and M show divalent, six valent and five valent metal ions,respectively, shows as singly or as complex solid solution with anotherA130 structure piezoelectric and electrostrictive properties.

The inventors have found out that Pb(W l\ia )O having the pervoskitestructure wherein W having M and Ma having l\i and representing at leastone element selected from the group consisting of Ni and Zn are locatedat the position B of A130 does not singly exhibit the piezoelectric andelectrostrictive properties in a manner similar to PbTiO but solidsolutions expressed by the formula wherein x=0.2 to 0.7, solid solutionsexpressed by the formula (VI/'2 A131,?) wherein Mb represents at leastone element selected from the group consisting of Zr and Sn, and x=0.02to 0.7,

y=0.l to 0.8, $20 to 0.75 and x+ *+z=l.0, and solid solutions expressedby said formulas wherein from zero to 20 atoms percent of Pb is replacedby at least one alkaline earth element selected from the groupconsisting of Ba, Ca and Sr and further containing Mn at a ratecorresponding to up to 5.0 weight percent of MnO in the aggregateconspicuously improve the mechanical quality factor Qm.

The principal object of the invention is to provide a novel and usefulpolarizable ferroelectric ceramic composition suitable for use inelectromechanical transducer elements.

Another object of the invention is to provide a polarizableferroelectric ceramic composition having a very high mechanical qualityfactor.

The invention will be explained with reference to the followingexamples.

EXAMPLE 1 PbO, W03, Z110, Tloz, Zl'Og, S1102, BHCOQ, CaCO and SrCO; wereadmixed and ground such that ceramics having compositions shown in thefollowing Tables 1 and 2 were obtained. Then the product thus obtainedwas molded and calcined at a temperature of 700 to 1,000 C. and thenground again and sintered in PbO atmosphere at a temperature of 1,100 to1,400 C. to obtain a disk having a diameter of about 20 mm. and 0.8 mm.in thickness. This disk thus obtained was electroded at each mainsurface with a silver electrode and polarized for one hour by applying adirect current electric field of 3.2 kv. (4O kv./cm.) at a temperatureof 80 C. This disk thus treated was stored in the air at roomtemperature for one week and then the electromechanical couplingcoefficient kp. and dielectric constant e of the disk were measured. Theresults thus obtained were shown in the following Tables 1 and 2.

TABLE 1 Electromechanical coupling coetfi- Dielectric cient, eonstant,kp. e

Composition (molar ratio) PDQVt-g-Nlg-QO; lbTiO; PbY-rO;

PlJSllO3 Sample No:

place of Pb(Wi/2-Nl 0 TABLE 2 D ielectric. constant,

Composition hp. 2

or xPb(W -Ma )O yPbTiO zPbMbO wherein up to 20 atom percent of Pb isreplaced by at least one alkaline earth element selected from the groupconsisting of Ba, Ca and Sr showed at least 0.1 of electromecharicalcoupling coefiicient kp. and at least 300 of dielectric constant e andwere suitable for use in practice as piezoelectric and electrostrictiveceramics. The range of x=0.09 to 0.45, y::0.25 to 0.65, z=0.25 to 0.6and .r+y+z=l.0 exhibiting more than 0.3 of electromechan- EXAMPLE 2 PbO,W0 NiO, TiO- and ZrO were admixed such that the basic compositionexpressed by the formula, O-3Pb(V1 2'Ni1 2)O30.5PbTiO -0.2PbZrO \VasObtained. The composition thus obtained was further added with MnO andground. The product thus obtained was molded and calcined at atemperature of 700 to 900 C. and then ground again and molded andsubsequently sintered in PbO atmosphere at a temperature of 1,000 to1,300 C. to obtain a disk having a diameter of about 20 mm. and 0.8 mm.in thickness. This disk was electroded at each main surface with asilver electrode and then polarized by applying direct current electricfield of 3.2 kv. (4O kv./cm.) at a temperature of 80 C. for one hour.This disk was then stored in the air at room temperature for one weekand electromechanical coupling ooefiicient kp., dielectric constant eand mechanical quality factor Qm of the disk were measured. The resultsAs can be seen from the above Tables 4 and 5,

wherein Ma represents at least one element selected from coefficient kp.which can practicably be used as piezoelectric and electrostrictiveceramics and of remarkably improving mechanical quality factor Qm.Particularly, the range of x=0.05 to 0.6, y=0.l to 0.8, z= to 0.6 andx+y+z=l.0 is preferable, because such range makes it possible to improvethe mechanical quality factor Qm twice as large as that without addingMnO Manganese may be added in the form of metals, oxides or othercompounds. Manganese may be added at a ratio corresponding to front 0 to5.0 weight percent of MnO in the aggregate. In this case it ispreferable to increase the amount of lead such that lead becomes inbalance with manganese added.

Pb(W Ma )O PbTiO and PbMbO each constituting the basic compositionaccording to the invention have perovskite structure expressed by theformula, A80 respectively, and do not individually exhibit piezoelectricand electrostrictive properties, but exhibit, when formed into complexsolid solutions expressed by the formulas,

wherein x=0.02 to 0.7, y=0.1 to 0.8, 2 0 to 0.75 and x+y z=1.0,piezoelectric and electrostrictive properties.

When a part of Pb in the above composition of IPb(W1 2 Ma1 2)O Or xPb-(W -Ma )O -yPbTiO zPbMbO is substituted with at least one alkaline earthelement selected from the group consisting of Ba, Ca and Sr, the rate ofthe substitution is to be less than 20 atom percent, because asubstitution in excess of 20 atom percent causes remarkabledeterioration of piezoelectric properties of products.

The ceramic composition according to the invention, when expressed bythe above mentioned formulas, exhibits the highest piezoelectric andelectrostrictive properties.

But it is difficult in practice to obtain the atomic ratio as strictlydefined by the above mentioned formulas even if sintering treatment iseffected in specially adjusted atmosphere or the amount of theingredients to be added is increased beforehand in order to compensatefor vaporization of the ingredients during sintering of the ceramiccomposition. Some deviation from the above mentioned atomic ratio isallowable since the ceramic com position according to the invention isnot substantially influenced by such deviation.

What we claim is:

1. A polarizable ferroelectric ceramic composition consistingessentially of a compound expressed by the form- 2. A polarizableferroelectric ceramic composition consisting essentially of a compoundexpressed by the formula, .rPb(W -Mai )O yPbTiO -zPbMbO wherein Marepresents at least one element selected from the group consisting of Niand Zn, Mb represents at least one element selected from the groupconsisting of Zr and Sn, and 2. 0.02 to 0.7, y=0.1 to 0.8, 2:0 to 0.75and x+y+z=1.0.

3. A polarizable ferroelectric ceramic composition as claimed in claim 2wherein up to atom percent of Pb is replaced by at least one alkalineearth element selected from the group consisting of Ba, Ca and Sr.

4. A polarizable ferroelectric ceramic composition consistingessentially of a compound expressed by the formula, -hl'ln Mb representsat least one element scl-..cted f om the group consisting of Zr and Sn,and x==0.02 to 0.7, 1 0.1 to 0.8, 2:0 to 0.75 and x+y+Fl.0.

5. A polarizable ferroelectric ceramic composition as claimed in claim 4wherein up to 20 atom percent of Pb is replaced by at least one alkalineearth element selected from the group consisting of Ba, Ca and Sr.

Ma represents at least one element selected from the group consisting ofNi and Zn, Mb represents at least one element selected from the groupconsisting of Zr and Sn, and x=0.02 to 0.7, 3 :01 to 0.8, 2 0 to 0.75and x-l-y+z=l.0, said composition including, as a substituent for anequivalent amount of lead therein, from zero to 20 atom percent, in theaggregate, of at least one alkaline earth element selected from thegroup consisting of Ba, Ca and Sr, and further containing manganese inan amount corresponding to from zero to 5.0 weight pet'- cent of MnO inthe aggregate.

6. A polarizable ferroelectric ceramic composition consistingessentially of a compound expressed by the formula, xPb(W -Zn )O yPbTiO-:PbMbO wherein Mb represents at least one element selected from thegroup consisting of Zr and Sn, and x 002 to 0.7, y=0.l to 0.8, 1:0 to0.75 and x+y+z=1.0.

7. A polarizable ferroelectric ceramic composition as claimed in claim 6wherein up to 20 atom percent of Pb is replaced by at least one alkalineearth element selected from the group consisting of Ba, Ca and Sr.

8. A polarizable ferroelectric ceramic composition consistingessentially of a compound expressed by the formula, xPb(W 'ri )O(1x)PbTiO wherein 2. 0.2 to 0.7.

9. A polarizable ferroelectric ceramic composition as claimed in claim 8wherein up to 20 atom percent of Pb is replaced by at least one alkalineearth element selected from the group consisting of Ba, Ca and Sr.

10. A polarizable ferroclectric ceramic composition consistingessentially of a compound expressed by the formula, .rPb(W -Zn )O 'PbTiO-zPbMbO wherein Mb represents at least one element selected from thegroup consisting of Zr and Sn, and x=0.09 to 0.45, y'=0.25 to 0.65,z=0.25 to 0.6 and x+y+z=1.0.

11. A polarizable ferroelectric ceramic composition as claimed in claim10 wherein up to 20 atom percent of Pb is replaced by at least onealkaline earth element selected from the group consisting of Ba, Ca andSr.

12. A. polarizable ferroelectric ceramic composition consistingessentially of a compound expressed by the formula, xPb(W -Ni )O yPbTiO-zPbMbO wherein Mb represents at least one element selected from thegroup consisting of Zr and Sn, and x=0.09 to 0.45, 0.25 to 0.65, z=0.25to 0.6 and x+y+z=1.0.

13. A polarizable ferroelectric ceramic composition as claimed in claim12 wherein up to 20 atom percent of Pb is replaced by at least onealkaline earth element selected from the group consisting of Ba, Ca andSr.

14. A polarizable ferroelectric ceramic composition consistingessentially of a compound expressed by the form- 15. A polarizableferroelectric ceramic composition consisting essentially of a compoundexpressed by the formula,

form ula,

wherein Ma represents at least one element selected from the groupconsisting of Ni and Zn, Mb represents at least one element selectedfrom the group consisting of Zr and Sn, and x=0.02 to 0.7, y=0.1 to 0.8,2:0 to 0.75 and x+y+z=1.0, and further containing manganese in an amountcorresponding to up to 5.0 weight percent of MnO in the aggregate.

17. A polarizable ferroelectric ceramic composition as claimed in claim16 wherein up to Z atom percent of Pb is replaced by at least onealkaline earth element selected from the group consisting of Ba, Ca andSr.

18. A polarizable ferroelectric ceramic composition consistingessentially of a compound expressed by the formula,

wherein Mb represents at least one element selected front the groupconsisting of Zr and Sn, and x=0.05 to 0.6, y==0.1 to 0.8, z=0 to 0.6and x+y+z=l.0, and further containing manganese in an amountcorresponding to from 0.05 to 5.0 weight percent of MnO in theaggregate.

19. A polarizable ferroelectric ceramic composition as claimed in claim18 wherein up to 20 atom percent of Pb is replaced by at least onealkaline earth element selected from the group consisting of Ba, Ca andSr.

20. A polarizable ferroelectric ceramic composition consistingessentially of a compound expressed by the formula,

xPb(\V 2111 2) wherein Mb represents at least one element selected fromthe group consisting of Zr and Sn, and x=0.05 to 0.6, :01 to 0.8, z=0 to0.6 and x+y+z=1.0, and further containing manganese in an amountcorresponding to from 0.05 to 5.0 weight percent of MnO in theaggregate.

21. A-polarizable ferroelectric ceramic composition as claimed in claim20 wherein up to 20 atom percent of Pb is replaced by at least onealkaline earth element selected from the group consisting of Ba, Ca andSr.

22. A polarizable ferroelectric ceramic composition consistingessentially of a compound expressed by the formula,

wherein Mb represents at least one element selected from the groupconsisting of Zr and Sn, and .t'=0.05 to 0.6, y=0.1 to 0.8, z=0 to 0.6and x-i-y{-z=l.0, and further containing manganese in an amountcorresponding to about 0.5 weight percent of MnO in the aggregate.

23. A polarizable fcrroelectric ceramic composition as claimed in claim22 wherein up to 20 atom percent of Pb is replaced by at least onealkaline earth element selected from the group consisting of Ba, Ca andSr.

24. A polarizable ferroelectric ceramic composition consistingessentially of a compound expressed by the formula,

xPb(W1/2Zn1 2)O3)'PbTiO --ZPbh bO3 wherein Mb represents at least oneelement selected from the group consisting of Zr and Sn, and x=0.05 to0.6, y=0.l to 0.8, 1 0 to 0.6 and x+)'-i2=l.0, and further containingmanganese in an amount corresponding to about 0.5 weight percent of MnOin the aggregate.

25. A polarizable ferroelectric ceramic composition consistingessentially of a compound expressed by the formula,

References Cited UNITED STATES PATENTS 3,372,121 3/1968 Banno 25262.9

TOBIAS E. LEVGW, Primary Examiner I. COOPER, Assistant Examiner US. Cl.X.R. 10639 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3 ,463 ,732 August 26 1969 Hisao Banno et a1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, line 9,

"4l/S5,798" should read 4l/74,0S4 Column 2, line 4,

2+ 5 M h 1d d 5 cu rea M 5/3 Columns 3 and 4, TABLE 1, fourth column,line 32 thereof "0.1" should read 0.4 Columns 5 and 6, TABLE 4, eiththcolumn,]

16 thereof, "850" should read 857 Signed and sealed this 10th day ofNovember 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

